The invention relates to acoustic wave detectors and more particularly to the use of a compact optical-fiber sensor assembly for the detection of sound waves in a fluid medium.
Heretofore sound waves have been detected by different types of electromechanical devices such as capacitance microphones and piezoelectric and magnetostrictive transducers. These yield an electrical output signal when exposed to incident sound waves. Such devices provide a means for directly obtaining an electrical signal that varies in time in the same way that the pressure varies in the sound field. Some of the disadvantages of such systems are that they are bulky, expensive and require impedance matching between the sound detector and transmission and signal processing system.
Optical waveguides and optical fibers have been used for conducting optical radiation from one point to another. Uses of such systems have been contemplated in the communication field for communicating optical signals and messages from one place to another. Other systems make use of stress applied to an optical fiber to modulate the optical radiation as it is transmitted through the fiber (for instance, see U.S. Pat. No. 4,068,191).
One system, which makes use of an optical fiber coil through which optical radiation is transmitted, is disclosed in U.S. Pat. No. 2,972,051. This patent is for the detection of ionizing radiation which permanently changes the optical index of the optical fiber. Further, use of such a system has been set forth by George H. Segal et.al. in an article "New Real Time Dosimeters Use Fiber Optics" in Naval Research Laboratory and Development Highlights, Vol. 1, pp. 7 and 8, December 1974.
Optical fibers, one in the water and one not in the water, in the form of a double-path optical interferometer have been used for detecting acoustic waves in a sound medium as set forth in U.S. Pat. No. 4,162,397. This patent teaches the use of a single optical fiber in the sound-field medium where the acoustical waves interact with the single optical fiber. The detector is affixed by temperature changes which is detected as noise.